Laser printers that employ fusing technology where a toner is heated to a malleable state for subsequent introduction to and bonding with a media substrate are commonly used in producing printed documents. In a typical desktop-type laser printer used in association with a computer, a fusing roller and a pressure roller work in cooperative unison to respectively provide thermal energy for making the toner malleable and provide pressure to force the malleable toner into fibers of the media substrate for permanent adherence. Inside the fusing roller is a heater that typically comprises a ceramic substrate with an electrical heating circuit provided thereon. The heater has one heat zone that extends substantially the entire length of the roller such that equal heat is emitted along this entire roller length.
When a typical sheet of paper having a usual width of about 8.5 inches is introduced between the fusing and pressure rollers in a normal print mode, the fusing roller, which has about the same width as the paper, provides heat for toner softening as printing occurs evenly over the width of the sheet.
Applicant has, however, discovered a number of problems with current fuser design. For example, where the printed media is narrower than the length of the fusing roller, the thermal energy emitted by the fusing roller lateral to the narrower media (e.g. an envelope) may become quite high and can create a significant thermal stress condition in the heating element at those sites outside the media dimensions. When combined with cyclical stresses induced by the on-off cycle of the printer and with roller mechanics in general, stress fractures and cracks can form in the heater. Should a crack form across the ceramic substrate causing a break in the associated electrical circuit, the printer may malfunction or entirely cease operation. Presently, a relatively thick, costly, and thermally inefficient ceramic heating element which is capable of withstanding considerable thermal stress is used in most printers.
Further, this thermal energy emitted lateral to the media to be printed can cause melting and deformation of any nearby plastic components of the printer mechanism or housing. In addition to causing printer damage and/or shut-down, these elevated temperatures can also adversely affect product quality. In particular, too much moisture may be driven out of the edges of the narrower media by the adjoining high heat. When this occurs, excessive media curl or wave caused by differences in moisture content across the media, develop and produce a product of substandard appearance. Presently, some printers employ a temperature monitor within the printer. When a sufficiently high temperature is reached, the monitor either slows or stops the printing process, an event that is not welcomed by a user.
Finally, electrical energy is wasted by most current printers during printing of smaller width media.